Clean up old pref migrations

One of the migrations is bound to a bug that is still open so added
appropriate comment and left the migration in for now.

BUG=none

Change-Id: I92f9987b768da5b446be0dcd06465e0b3489fafd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2784626
Auto-Submit: Julian Pastarmov <[email protected]>
Commit-Queue: Gabriel Charette <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Cr-Commit-Position: refs/heads/master@{#867597}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 414d168..2b3bd206b 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -430,10 +430,6 @@
 
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 
-// Deprecated 3/2020
-const char kDataReductionNetworkProperties[] =
-    "data_reduction.network_properties";
-
 #if BUILDFLAG(IS_CHROMEOS_ASH)
 // Deprecated 4/2020
 const char kAmbientModeTopicSource[] = "settings.ambient_mode.topic_source";
@@ -598,8 +594,6 @@
 // Register prefs used only for migration (clearing or moving to a new key).
 void RegisterProfilePrefsForMigration(
     user_prefs::PrefRegistrySyncable* registry) {
-  registry->RegisterDictionaryPref(kDataReductionNetworkProperties);
-
 #if BUILDFLAG(IS_CHROMEOS_ASH)
   registry->RegisterDictionaryPref(kSupervisedUserAllowlists);
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
@@ -1266,7 +1260,8 @@
   syncer::MigrateSyncSuppressedPref(profile_prefs);
 
   // Added 3/2020.
-  profile_prefs->ClearPref(kDataReductionNetworkProperties);
+  // TODO(crbug.com/1062698): Remove this once the privacy settings redesign
+  // is fully launched.
   chrome_browser_net::secure_dns::MigrateProbesSettingToOrFromBackup(
       profile_prefs);